Passivation of GaAs FET's with PECVD silicon nitride films ofdifferent stress states

The passivation of GaAs MESFETs with plasma-enhanced chemical-vapor-deposited (PECVD) silicon nitride films of both compressive and tensile stress is reported. Elastic stresses included in GaAs following nitride passivation can produce piezoelectric charge density, which results in a shift of MESFET characteristics. The shift of MESFET parameters due to passivation was found to be dependent on gate orientation. The experiments show that nitride of tensile stress is preferable for MESFETS with [011-bar] oriented gates. The shifts in V_TH,I_DSS, and G_M of the devices before and after nitride passivation are less than 5% if the nitride of appropriate stress states are used for passivation. The breakdown voltage of the MESFETs after nitride deposition was also studied. It is found that the process with higher hydrogen incorporation tends to reduce the surface oxide and increase the breakdown voltage after nitride deposition. In addition, the passivation of double-channel HEMTs is reported for the first time     

A bibliography on silicon nitride films

A bibliography of ca. 600 references on the preparation, properties and applications of silicon nitride (Si₃N₄) films has been collected from the literature.The bibliography comprises a list of papers appearing in Chemical Abstracts, journals, conference proceedings and patent abstracts, covering the period from 1966 (when the first article appeared describing an application of silicon nitride films in the solid state technology) through to 1978.     

Processing and characterisation of PECVD silicon nitride films

Amorphous Si-N films are synthesised from an NH₃/SiH₄ gas mixture by plasma-enhanced chemical vapour deposition (PECVD) at fixed radio frequency (13.56 MHz) and total gas pressure (34 ± 4 Torr). The variable process parameters and their ranges are: (i) substrate temperature, 200–400°C; (ii) RF power density, 0.08–0.35 W cm⁻²; (iii) NH₃/SiH₄ flow ratio, 40:400–40: 1200 ml min⁻¹. Fundamental properties of the Si-N films are characterised through elemental composition, chemical speciation, optical and electrical properties, all of which are dependent on the process parameters.     

Determination of local stress in PECVD nitride films

Silicon nitride and silicon oxynitride films grown on silicon substrates by plasma-enhanced chemical vapour deposition (PECVD) are stressed and the correlation of the film stress to its refractive index is presented. It is shown that it is possible to determine the stress of the PECVD nitride films by measuring their refractive indices, which can be done locally, but that the method is not applicable to the PECVD oxynitride films.     

Photoluminescence spectroscopy of sputtering Er-doped silicon-rich silicon nitride films

Er-doped silicon-rich silicon nitride (SRN) films were deposited on silicon substrate by an RF magnetron reaction sputtering system. After high temperature annealing, the films show intense photoluminescence in both the visible and infrared regions. Besides broad-band luminescence centered at 780 nm which originates from silicon nanocrystals, resolved peaks due to transitions from all high energy levels up to ~2H_(11/2) to the ground state of Er~(3+) are observed. Raman spectra and HRTEM measurements have been performed to investigate the structure of the films, and possible excitation processes are discussed.     

磁控溅射掺铒富硅氮化硅薄膜的光致荧光谱

Er-doped silicon-rich silicon nitride （SRN） films were deposited on silicon substrate by an RF magnetron reaction sputtering system. After high temperature annealing, the films show intense photoluminescence in both the visible and infrared regions. Besides broad-band luminescence centered at 780 nm which originates from silicon nanocrystals, resolved peaks due to transitions from all high energy levels up to 2H11/2 to the ground state of Er^3＋ are observed. Raman spectra and HRTEM measurements have been performed to investigate the structure of thefilms, and possible excitation processes are discussed.     

Mechanical stability of PECVD silicon nitride protective films over bondwires, bonds and bondpads during thermal stress

PECVD silicon nitride thin films have potential application as protective diffusion barriers against water and aggressive ions which might corrode aluminum bondpads, bonds, and bondwires in packaged microelectronic assemblies. Test articles representing mounted and bonded devices were coated with silicon nitride films of thicknesses from 50 to 20,000 Å, then subjected to temperature and chemical stresses. These thin films exhibited less tendency to crack under temperature stress than would be predicted based on the physical properties of bulk silicon nitride. Films of less than one micron thickness over Al structures did not crack under standard industrial temperature cycling and showed good coverage near the bond interfaces and around the bondwires. The spread of Al metallization corrosion under these films proceeded at a slower rate beneath the thinner films due to their more favorable mechanical properties. Although the intrinsic stresses could not be measured, the decreased tendency for the thinner films to crack is primarily a result of higher ultimate strain and not initial compressive stresses.     

Measuring stiffnesses and residual stresses of silicon nitride thin films

The mechanical deflection of circular membranes of SiN _x is presented as a technique for measuring the stiffness and residual stress of very thin, single-layer films. The dimensions of the membranes are controlled precisely using standard photolithography, dry etching and wet etching techniques. Thicknesses vary between 0.09 μm and 0.27 μm and average diameters range between 1100 μm and 4100 μm. A Nanoindenter is used to deflect the membranes with a point force at their centers, and to continuously record the applied forces and the resulting deflections. The analysis of the force-deflection data yields the values of Young’s moduli and residual stresses for the films.     

Analyses for stoichiometry and for Hydrogen and Oxygen in silicon nitride films

Optical, ion, and electron probe techniques can be effectively applied to analyze for H, O, and the Si/N ratio in thin films of silicon nitride. The films studied were formed by chemical-vapor deposition or plasma deposition for application as a gate dielectric in semiconductor memory devices and for circuit encapsulation. The H concentration is measured by the multiple internal reflection technique which detects NH and SiH vibrational modes. A decrease in SiH bonding with an increase in deposition temperature is shown for chemical-vapor-deposited silicon nitride, and a very high concentration of SiH bonds is observed in plasma-deposited silicon nitride. Ion back-scattering analysis is a direct method for measuring the Si/N ratio and a related nuclear reaction analysis technique is a direct method for measuring and profiling the O content. Backscattering analysis shows a significantly larger Si/N ratio for plasma than for chemical-vapor-deposited silicon nitride. The O profile obtained by reaction analysis for a nitride/oxide/Si structure is compared to that obtained by sputter Auger electron spectroscopy, and the results show that O concentrations down to ∼0.5 at % can be measured by either technique. Auger analysis gives better depth resolution than reaction analysis but it requires a calibration standard. Auger results also show N penetration of interfacial SiO2and accumulation of N at the Si-SiO2interface.     

Nonempirical simulation of chemical deposition of silicon nitride films in CVD reactors

This work is devoted to the atomistic simulation of chemical vapor deposition (CVD) of thin silicon nitride films from the mixture of dichlorosilane (DCS) and ammonia in CVD reactors. The earlier developed chemical mechanism is substantially extended by including the reactions of catalytic decomposition of DCS, and a self-consistent atomistic model of a CVD process is developed. An extended chemical mechanism is constructed and analyzed that allows one to adequately describe kinetic processes in a gas phase within the ranges of temperature, pressure, and the DCS: NH₃ ratio of original reactants, that are characteristic of silicon nitride deposition. An effective kinetic model is developed that involves the calculation of the rate constants and the concentrations of the gas mixture components. A thermodynamic analysis of the surface coverage by various chemisorbed groups is carried out, and equilibrium surface concentrations are obtained for the main chemisorbed groups. Practically significant conclusions are made about the character of the deposition process and, in particular, about the role of the extended chemical mechanism.     

低应力非晶硅薄膜的制备

本文研究了三种降低非晶硅材料应力的手段:优化工艺参数.通过N2退火,将非晶硅的压应力变为张应力.通过额外的掺杂硼来改变非晶硅的应力.最初加入硼掺杂后应力会发生突变,但随着同步掺杂的浓度增加,最终的应力变化会趋向缓和.通过综合利用以上三个手段,最终的实际结果达到了预定的低应力目标.     

Formation of silicon nitride films by remote plasma-enhanced chemical vapour deposition

In this paper we describe the growth of silicon nitride from nitrogen and silane for the first time by capacitively coupled remote PECVD. We report on the effect of process parameters on the composition and properties of the deposited films and we show that by adjustment of these parameters it is possible to produce high-quality material which could be of interest for electronic applications. Of particular note is that the growth rate is about one order of magnitude higher than any previously reported for nitride growth with remote PECVD using molecular nitrogen as the nitrogen source. We also discuss the mechanism of growth and propose that electron excitation of nitrogen and silane occurs in the gas phase, producing SiH_x species which are adsorbed on the growing surface. The nitrogen is then incorporated into the layer by heterogeneous reaction.     

Trapping levels in silicon nitride

The trapping levels in silicon nitride have been investigated using the thermally stimulated current technique. Traps at between 0.50 and 0.90eV below the conduction band of the nitride were found, as well as a distribution of traps at and near the silicon-silicon nitride interface about 0.10eV below the conduction band of the silicon.     

New applications of low temperature PECVD silicon nitride films for microelectronic device fabrication

Silicon nitride has been widely used in microelectronic device fabrication processes for encapsulation, surface passivation and isolation. In this paper we report new applications of plasma-enhanced chemical vapor deposition (PECVD) silicon nitride films that can be deposited at a temperature lower than the soft bake temperature of normal photoresists. Lift-off of the silicon nitride film was carried out using standard positive photoresist. GaAs MESFETs and InP MISFETs with self-aligned gates were successfully fabricated using this lift-off process of low temperature PECVD silicon nitride.     

Stress control of silicon nitride films deposited by plasma enhanced chemical vapor deposition

Stress controllable silicon nitride(Si Nx) films deposited by plasma enhanced chemical vapor deposition(PECVD) are reported. Low stress Si Nx films were deposited in both high frequency(HF) mode and dual frequency(HF/LF) mode. By optimizing process parameters, stress free(-0.27 MPa) Si Nx films were obtained with the deposition rate of 45.5 nm/min and the refractive index of 2.06. Furthermore, at HF/LF mode, the stress is significantly influenced by LF ratio and LF power, and can be controlled to be 10 MPa with the LF ratio of 17% and LF power of 150 W. However, LF power has a little effect on the deposition rate due to the interaction between HF power and LF power. The deposited Si Nx films have good mechanical and optical properties, low deposition temperature and controllable stress, and can be widely used in integrated circuit(IC), micro-electro-mechanical systems(MEMS) and bio-MEMS.     

Diffusional creep induced stress relaxation in thin Cu films on silicon

The results of stress measurements during annealing of thin copper films deposited on 100 μm Si substrates are presented. The stress in thin films was determined by using an optical system for curvature measurements. The annealing experiments were done during thermal cycles of heating and cooling procedures from room temperature up to 400 °C with a rate 10 °C/min. The total thickness of thin films was between 20 and 100 nm. The obtained results showed that the difference between the end and the initial values of the ratio of force to width increases with the thickness of the samples. The initial linear shape of the temperature-stress plots reaches higher temperature values with an increase in film thickness. In order to explain the observations, the dependence of stress on temperature was calculated using the rate of Coble creep. It was found that the theoretical curves reveal the same features as the experimental data. It was concluded that diffusional creep mechanism dominates for thin film of thickness below 100 nm.     

Modeling the growth of PECVD silicon nitride films for solar cellapplications using neural networks

Silicon nitride films grown by plasma-enhanced chemical vapor deposition (PECVD) are useful for a variety of applications, including anti-reflection coatings in solar cells, passivation layers, dielectric layers in metal/insulator structures, and diffusion masks, PECVD nitride films are known to contain hydrogen, and defect passivation by hydrogenation enhances efficiency in polycrystalline silicon solar cells. PECVD systems are controlled by many operating variables, including RF power, pressure, gas flow rate, reactant composition, and substrate temperature. The wide variety of processing conditions, as well as the complex nature of particle dynamics within a plasma, makes tailoring Si₃N₄ film properties very challenging, since it is difficult to determine the exact relationship between desired film properties and controllable deposition conditions. In this study, silicon nitride PECVD modeling using neural networks has been investigated. The deposition of Si₃N₄ was characterized via a central composite experimental design, and data from this experiment was used to train optimized feed-forward neural networks using the back-propagation algorithm. From these neural process models, the effect of deposition conditions on film properties has been studied. It was found that the process parameters critical to increasing hydrogenation and therefore enhancing carrier lifetime in polysilicon solar cells are temperature, silane, and ammonia flow rate. The deposition experiments were carried out in a Plasma Therm 700 series PECVD system     

Optical characterization of Si-rich silicon nitride films prepared by low pressure chemical vapor deposition

An investigation of the optical properties of Si-rich silicon nitride films prepared by low pressure chemical vapor deposition (LPCVD) from dichlorosilane (SiH₂Cl₂, DCS) and ammonia (NH₃) mixtures has been performed. From TEM analysis, it was found that the excess Si forms nanocrystals the size of which depends on the temperature. The real and the imaginary part of the refractive index of the films were calculated using spectroscopic ellipsometry by fitting the ellipsometric data in the range 1000–250 nm using the Tauc–Lorentz model. It was found that the optical constants of the films mainly depend on their chemical composition which can be controlled by the DCS/NH₃ flow ratio. Annealing at temperatures up to 1100 °C for 4 h does not considerably affect the refractive index of the films. Depending on their stoichiometry and the annealing conditions applied after growth, some of the films emitted light in the visible at room temperature. This was attributed to the quantum confinement of carriers in the Si nanocrystals contained in the films.     

Electron spin resonance and photoluminescence in pyrolytic silicon nitride films irradiated with argon and molecular ions

The photoluminescence and electron spin resonance phenomena are studied at room temperature for pyrolytic silicon nitride films irradiated with argon ions or molecular nitrogen ions and annealed at temperatures in the range 500–1100°C. The absorption spectrum suggests that the broad photoluminescence band at 400–600 nm is due to electron transitions between the band tails. The low-dose irradiation with argon ions slightly reduces the photoluminescence intensity, whereas the high-dose irradiation followed by annealing at 800–900°C can induce a more than twofold increase in the intensity. At the same time, irradiation with nitrogen ions profoundly suppresses the integrated photoluminescence intensity that decreases by more than an order of magnitude. A correlation between the changes in the photoluminescence intensity and the amplitude of the ESR spectra on annealing of the silicon nitride films is observed.